Cycloaddition Reactions of Indenes. 3. 1:1 Adduct from 1,1-Dimethyl-1H-indene and Dimethyl Acetylenedicarboxylate

Article abstract of DOI:10.1021/jo00320a017

In contrast to 1H-indene (1a) and 1-methyl-1H-indene (1b), wich give stable 1:2 adducts (3a, 34percent; 3b, 30percent) and with 1a also a 1:3 adduct (4a; 40percent from 1a; 71percent from 3a) with dimethyl acetylenedicarboxylate (DMAD), 1,1-dimethyl-1H-indene (1d) and DMAD gave as the only crystalline product a cycloadduct of different structural type, dimethyl 1a,7b-cis-dihydro-1,1-dimethyl-1H-cyclopropanaphthalene-2,3-dicarboxylate (5a, 14percent), the structure of which has been confirmed by X-ray crystallography.